The present invention relates to pumps, and more particularly to molten metal pump apparatus and methods for assembling and disassembling such apparatus.
There are three basic types of molten metal pumps described in detail in prior U.S. Pat. No. 5,203,681. Generally, a molten metal pump comprises a centrifugal pump modified to provide processing of the molten metal.
The pump typically includes a base or casing having a pumping chamber and an impeller received within the chamber. The base includes inlet and outlet passages for intake and discharge of molten metal being pumped. The pump base together with the impeller are submerged in the molten metal, supported on the bottom of the vessel containing the molten metal. The pump base is connected by refractory cement and/or mechanical arrangements to a plurality of vertically extending members such as risers for conveying molten metal from the vessel and support posts connected to a drive arrangement positioned above the level molten metal. In typical installations, these vertically extending members may be several feet long, e.g. one to four feet in length or longer, in order to provide adequate clearance above the molten metal level. For convenience, the invention is discussed below with particular reference to posts.
The portions of the pump submerged in the molten metal are directly contacted and exposed to the harsh conditions thereof, and they are formed of refractory materials such as graphite, silicon carbide, alumina, zirconia or hexalloy. For example, the submerged components of the pump including the posts may be made of graphite. The posts extend through the level of the molten metal and they are connected to a motor mounting plate which may include a metal plate strength member and a lower insulation layer to protect the motor from the heat of the molten metal.
In prior art arrangements, downwardly opening post sockets are fixed to the motor mounting plate and receive the upper ends of the posts. One or more post sockets may be fixed to a post support plate, as by welding, and the support plate is secured to the motor mounting plate.
A threaded fastener extends through a clearance opening in the motor mounting plate and/or post support plate for threaded engagement with the post along its longitudinal axis. The post may also be secured within the post sockets by means of a refractory cement.
Such prior art arrangements are not entirely satisfactory. The downwardly opening post sockets are often contaminated with splashing molten metal. Also, the quality of the post connection was substantially dependent upon the single threaded fastener. A most significant disadvantage is the need to remove the post support plate and/or the motor mounting plate when it is necessary to replace the post. Such disassembly is time-consuming and results in considerable downtime.
An improved post mounting structure and assembly/disassembly technique are provided. In accordance with the invention, a more effective post connection is provided that facilitates disassembly. To that end, the post and mounting plate together with any related structural members are dimensioned to allow relative movement of these components upon decoupling them during disassembly.
In accordance with one aspect of the invention, it is not necessary to disassemble the motor mounting plate and/or post support plate for installation and removal of a post.
In accordance with another aspect of the invention, a post mounting coupling compressively grips the post to reinforce the end of the post. This coupling may have a monolithic construction that assures proper alignment of the coupling as it is connected to the end of the post.
In one of the illustrated embodiments, a post mounting passageway which may comprise one or more clearance bores is provided in the motor mounting plate and/or post support plate as well as any aligned insulation layer to permit passage of the post therethrough and into engagement with the pump base. The upper end of the post extends above the motor mounting plate and/or post support plate for engagement with a coupling secured to the mounting plate. The lower end of the post may be mounted to the base in a known manner by refractory cement and/or mechanical connections.
In another illustrated embodiment, the coupling is mounted to a lower surface of the mounting plate or post support plate, and a portion of the coupling extends upwardly through the clearance bore or bores. In such arrangements, the post may be of shorter axial length and the coupling is circumferentially reinforced by the mounting plate.
In another illustrated embodiment, the coupling is again mounted to the lower surface of the mounting plate or post support plate, and no clearance bore or bores are required in the latter. In such embodiment, the upper end of the post is received in the coupling below the level of the mounting plate or post support plate.
The coupling includes gripping members operable between a locked position engaging the upper post end and an unlocked position releasing the upper post end. Preferably, the gripping members have gripping surfaces shaped to correspond with the peripheral surface of the post end, e.g. arcuate gripping surfaces. The gripping members may be retained and/or moved by a locking member such as a mechanical fastener.
In the illustrated embodiment, The coupling comprises a split collar flange coupling that is monolithic and thereby aligns the post relative to the mounting plate and/or post support plate and the cooperating collar gripping portions. Accordingly, once the coupling is fixed to the mounting plate and/or post support plate, the proper axial alignment of the post is assured as well as the orientation and peripheral joint between the collar portions.
In the illustrated embodiments, the flange portion of the coupling is secured to the motor mounting plate and/or post support plate by threaded fasteners. The end of the post is received in the collar portion of the coupling. The split portions of the collar are drawn into tight engagement about the periphery of the post by a locking member. The locking member applies compressive gripping forces to the end of the post or riser, and it comprises a threaded fastener extending through the split portions of the collar and the post or associated pairs of ears radially extending from each split collar portion and secured together by threaded fasteners.
The coupling thereby fixes the longitudinal position and height of the post relative to the motor mounting plate and/or post support plate. The coupling also distributes the coupling or engagement load over substantially the entire circumferential area of the gripping surfaces or collar. In this manner, the prior art concentration of loads along a single threaded connection is avoided.
Advantageously, this distribution of the clamping load is achieved without the use of refractory adhesives. Instead, an easily disengaged and reengaged mechanical connection is used. However, adhesives may be used with the split collar flange coupling, if desired.
Also, it should be appreciated that the split collar flange coupling may be positioned above the motor mounting plate and/or post support plate so as to protect it from splashing molten metal. Further, the upwardly opening coupling orientation tends to inhibit entry therein of splashing molten metal.